Human Body Clock

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Questions and Answers

Explain the role of circadian rhythms in energy management during active and sleep phases.

Circadian rhythms help regulate energy expenditure by increasing it during the active phase and decreasing it during sleep, while promoting processes like cellular repair and memory consolidation during rest.

How have organisms evolved in response to the Earth's rotation and light/dark cycles?

Organisms have developed internal biological clocks that align with the Earth's rotation, allowing them to anticipate environmental changes and optimize their physiological functions.

Discuss the impact of disrupted circadian rhythms on human physiology.

Disrupted circadian rhythms can lead to inefficient energy expenditure, impaired metabolism, and issues with bodily functions such as digestion and immune response.

What are practical consequences of circadian rhythms on daily human activities such as eating and sleeping?

Circadian rhythms influence optimal times for eating and sleeping, promoting better digestion and sleep quality by aligning these activities with our biological clock. Signup and view all the answers

What mechanisms enable the body to adjust to changes in spatio-temporal niches due to circadian rhythms?

The body utilizes hormonal fluctuations, temperature regulation, and adjustments in organ function to adapt to changes in environment and maintain homeostasis. Signup and view all the answers

What is the primary environmental cue that helps reset circadian rhythms?

Light is the leading 'entrainment' cue. Signup and view all the answers

Define the term 'zeitgeber' in relation to circadian rhythms.

A zeitgeber is a time giver that helps entrain biological rhythms. Signup and view all the answers

What are the three criteria that define a biological rhythm as 'circadian'?

<ol> <li>An endogenous free-running period of approximately 24 hours, 2. Entrainability by external stimuli, 3. Temperature compensation.</li> </ol> Signup and view all the answers

How does disruption of sleep and circadian rhythm impact an individual's health?

It can adversely affect physiological, emotional, and cognitive health. Signup and view all the answers

What is the phenomenon where circadian rhythms slightly exceed a 24-hour cycle in constant conditions called?

It is referred to as a free-running period that lasts longer than 24 hours. Signup and view all the answers

Study Notes

Circadian Rhythms: Overview

Circadian rhythms are biological processes that occur in a roughly 24-hour cycle.
These rhythms are found in all life forms, including plants, insects, and mammals.
The primary source of rhythmicity is the internal clock located in an area of the brain.
Humans have a natural sleep-wake cycle as one form of circadian rhythm.
Other examples include hormones, temperature and metabolic rates.
Environmental factors such as light and temperature help regulate these biological clocks.

Circadian Rhythm: Biological Clocks

Biological clocks were first described in plants.
Sunflowers follow the sun throughout the day and turn back to the east nightly.
Plants have an internal biological clock regulating activity such as growth and photosynthesis.
Every cell in a plant has its own clock alongside the plant's.
Humans also have biological clocks in their cells.

Circadian Rhythm: The Human Body Clock

Human physiology is organised around a daily cycle of activity and sleep.
Almost all life on earth uses an internal biological clock
This anticipates changes resulting from light/dark cycles.
Internal synchronisation of processes, ensures activities happen at optimal times.
Energy expenditure is higher/food intake needed during active phase; digestive and repair processes decrease during sleep, but cellular repair and information processing increase.

Circadian Rhythm: Learning Outcomes

Understanding concepts of circadian function in biological clocks.
Identifying external cues essential to setting biological rhythms.
Recognizing examples of circadian rhythms in the body.
Characterising key hormones in circadian rhythms.
Defining molecular controls of circadian rhythms.
Understanding the significance of peripheral biological clocks.

Circadian Rhythm: A Brief History

All life on Earth adapts to the Earth's rotation around the sun.
External environmental factors change predictably.
Organisms, from algae to humans, evolve to regulate timekeeping according to light/dark cycles.
Different species inhabit varied temporal and spatial niches.
Physiology anticipates daily cycles (circadian rhythms).
Sleep-wake cycles are an example of circadian rhythms.

Circadian Rhythm: What is the Circadian Rhythm?

The circadian rhythm evolved to assist humans with adapting and anticipating environmental changes.
This includes adjustments in radiation, temperature, and food availability.
The body requires an internal circadian clock to optimise energy use.
Disruption to the circadian rhythm can have physiological, emotional, and cognitive consequences.

Circadian Rhythm: Entrainment

Circadian rhythms do not always precisely run on a 24-hour clock.
Without resetting, the sleep-wake cycles would shift later daily (by approximately ~10 mins).
Light is the main cue for entrainment.
The process of daily resetting is called photoentrainment.

Circadian Rhythm: Biological Rhythm Examples

A circadian rhythm needs to have an endogenous cycle of approximately 24 hours, it must remain consistent in constant conditions, and it can be entrained by external stimuli.
Rhythmically coordinated processes occur to ensure an optimal fitness of an individual.

Circadian Rhythm: Examples of Circadian Rhythm in Drosophila

Isolation of a gene in Drosophila demonstrates control of biological rhythm.
The protein accumulates during the night and is degraded during the day; this gene is an example of circadian rhythm.
Drosophila lays eggs in the morning;
Experiments show rhythms can persist even under constant light/dark conditions; these rhythms are still present, but shifted.
The circadian rhythm is reversible and can be reset.

Circadian Rhythm: Input Pathway & Output Pathway In Humans

Environmental cues interact with sensory receptors.
The master synchroniser, which is a part of the human brain, combines these cues.
This leads to outputs including physiological activity and hormonal release.
Light is the main synchronising component (Zeitgeber), which is used to reset the biological clock.

Circadian Rhythm: The Master Synchroniser: The SCN and Cellular Function

The SCN (suprachiasmatic nucleus) works as a master clock inside the brain.
Light-sensitive cells in the retina facilitate entrainment.
The SCN co-ordinates rhythms in many tissues through neural and endocrine signalling.
Without the SCN, body cell rhythms may gradually dissipate.

Circadian Rhythm: Day and Night

Light is a combination of different wavelengths within the visible spectrum, with blue light the most important.
OPSIN4 (light-sensitive photopigment) regulates a response to blue light, and this then affects melatonin secretion and promotes alertness.
Blue light from different sources (e.g., light bulbs, screens) suppresses the production of melatonin.

Circadian Rhythm: Hormones of the Circadian Rhythm: Melatonin

Melatonin is a hormone derived from tryptophan, crucial to regulating circadian rhythms.
Pineal gland secretes melatonin in response to light cues from retina via the SCN.
Melatonin rises at night to regulate sleep-wake cycles.
Blue light inhibits melatonin production.

Circadian Rhythm: Hormones of the Circadian Rhythm: Cortisol

Cortisol is a steroid hormone produced by adrenal glands.
It is released mostly during the day, influencing activity levels.
Cortisol is released during times of stress and/or low blood glucose.
Negative feedback mechanisms control cortisol release.

Circadian Rhythm: Coordinated Clock in Peripheral Tissues

Peripheral clocks in tissues are entrained, and function in synchrony with SCN, impacting rhythmic processes such as gene expression.
Gene and protein expression patterns regulate tissue function.

Circadian Rhythm: External Cues (Zeitgebers)

Light-dark cycles are powerful external zeitgebers.
Other zeitgebers include food, exercise and social cues.
Environmental temperature can also influence the biological clock.
These cues support synchronisation and entrainment.

Circadian Rhythm: Key Learning Points

Most living creatures employ an internal biological clock to regulate responses to light and darkness.
The synchronisation cues include eating, exercise and socialising, in addition to light and darkness.
The suprachiasmatic nucleus (SCN) co-ordinates peripheral clocks in the body.
Melatonin rises during the night and is suppressed by blue light.
Cortisol is secreted more in the day, in response to stress or low blood glucose.

Circadian Rhythm: Molecular Control of the Circadian Rhythm

The circadian rhythm involves a transcription/translation negative feedback loop involving 'clock' genes.
Clock genes produce proteins that regulate circadian processes including when other genes are expressed.
The levels of these clock proteins fluctuate cyclically.

Circadian Rhythm: Dysregulation

Shift work, jet lag, irregular sleep patterns, and certain lifestyle choices can negatively impact circadian rhythms.
Certain medical conditions can also result in circadian dysregulation.
Dysregulation can affect physical health, including bone mineralisation, and memory consolidation, and psychological health.

Circadian Rhythm: Rhythm Disorders

Misalignment between internal processes and external environments can disrupt various aspects of health.
This includes sleep, mental health and physical health, including neural and metabolic processes.
Gene mutations and environmental factors also contribute.

Circadian Rhythm: Affecting Drug Treatments

Drug metabolism and the timing of disease processes are impacted by circadian rhythms.
Some drugs are most effective when taken at specific times of the day.

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Description

Explore the fascinating world of circadian rhythms, which are biological processes operating on a 24-hour cycle in all life forms. This quiz delves into their mechanisms, including the role of the internal clock and environmental factors that influence these rhythms. Gain insights into human sleep-wake cycles and the biological clocks present in plants and animals.